Abstract

Frequency-dependent attenuation of ground motion in the Eastern United States is investigated for both vertical and horizontal components of motion. This is accomplished by digitizing and analyzing three-component, short-period Long Range Seismic Measurements data from over 200 earthquake-station pairs with epicentral distances less than about 1000 km. Pseudo-relative velocity as well as velocity response spectra, for 5 per cent damping, are obtained for the frequency range of 0.5 to 7 Hz. A multi-variate least-squares inversion is used to derive the station and source terms as well as the mean Q. Analysis of data for the entire Eastern United States indicates Q values for the vertical and horizontal components to be indistinguishable, substantial increase in Q with frequency (a factor of about 2 from 1 to 7 Hz), large (as much as a factor of 20 in amplitude) site terms for both the vertical and horizontal components, and the mean ratio of the peak horizontal to peak vertical component to be a stable characteristic of the site. Large regional variations in Q are also indicated by subsets of data such as for the Central United States and the Appalachian Mountains region.

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